Various fixes and improvements (#12878)

* Fix unused role routes being generated

* Remove unused JavaScript code

* Refactor filters code to be DRYer

* Fix `.count == 0` comparisons to `.empty?` in views

* Fix filters in views

app/views/relationships/show.html.haml

@@ -33,10 +33,9 @@
 
 = form_for(@form, url: relationships_path, method: :patch) do |f|
   = hidden_field_tag :page, params[:page] || 1
-  = hidden_field_tag :relationship, params[:relationship]
-  = hidden_field_tag :status, params[:status]
-  = hidden_field_tag :activity, params[:activity]
-  = hidden_field_tag :order, params[:order]
+
+  - RelationshipFilter::KEYS.each do |key|
+    = hidden_field_tag key, params[key] if params[key].present?
 
   .batch-table
     .batch-table__toolbar